No seriously, why would anyone need to hide their IP address from their financial transactions?
If you don't hide your IP address, you can be unmasked by tracking the IP as opposed to tracking your wallet address. Even with Darksend.
I'm talking with my grandmother and I'm trying to explain. Tell me like i need to explain it to my lovely old dear.
You send money to John.
When you send money to John, you announce to the network "Hey I'm sending money to John" and when you announce it you use your IP address to talk to the network. If you are on the network and listening you can go "Hey this guy is sending money to John from this IP address." Since your IP address is unique to you (at least your WAN IP is, for most people), it's easy to deduce who sent the payment if you have the tools available to you to do so.